The icon page (for instance, http://tg.dreamwidth.org/icons already does default to only showing I-think-50 icons at a time (why yes, we have been planning this for a while), so that definitely helps. The Edit Icons page doesn't paginate, so managing icons will be a bit more unwieldy, but I've been thinking about ways we can fix that without annoying the crap out of people who are looking to edit their icons in bulk.

EDIT, as soon as I hit post: unless, of course, you mean the pop-up visual icon browser that comes up when you're making a comment and hit 'browse' next to the icon dropdown! Yes, I've also been thinking about ways to make that a bit less unwieldy with large numbers of icons; I am starting to think the answer to all of the above may be to let people make "icon bundles" (grouped thematically, alphabetically, randomly, or however they want to group them) and let people first pick which 'bundle' they want to look into and only then display all the icons. I dunno, there's a lot of ways it could work. I wish we had more people who were experienced with clever UI design for complicated UI problems. :(